1. Field of the Invention
The present invention relates to an organic compound and a light-emitting element including the organic compound. The present invention also relates to a light-emitting device, an electronic device, and a lighting device each including the light-emitting element.
2. Description of the Related Art
In recent years, research and development have been extensively conducted on light-emitting elements using electroluminescence (EL). In a basic structure of such a light-emitting element, a layer containing a light-emitting substance is interposed between a pair of electrodes. By applying voltage to this element, light emission from the light-emitting substance can be obtained.
Such a light-emitting element is a self-luminous element and has advantages over liquid crystal displays, such as high visibility of pixels and no need of backlight; thus, such a light-emitting element is thought to be suitable as a flat panel display element. Besides, such a light-emitting element has advantages in that it can be manufactured to be thin and lightweight, and has very fast response speed.
Furthermore, since such a light-emitting element can be formed in a film form, planar light emission can be easily obtained; thus, a large-area element utilizing planar light emission can be formed. This feature is difficult to obtain with point light sources typified by incandescent lamps and LEDs or linear light sources typified by fluorescent lamps. Thus, the light-emitting element also has great potential as a planar light source applicable to a lighting device and the like.
Light-emitting elements utilizing electroluminescence are broadly classified according to whether they use an organic compound or an inorganic compound as a light-emitting substance. In the case where an organic compound is used as a light-emitting substance, application of voltage to a light-emitting element causes injection of electrons and holes from a pair of electrodes into a layer including the light-emitting organic compound, and thus current flows. The light-emitting organic compound is excited by the injection of carriers (electrons and holes), and emits light in returning to a ground state from the excited state (electrons and holes are recombined). The excited state formed by an organic compound can be a singlet excited state or a triplet excited state. Light emission from the singlet excited state is called fluorescence, and emission from the triplet excited state is called phosphorescence.
In improving element characteristics of such a light-emitting element, there are many problems which depend on substances used for the light-emitting element. Therefore, improvement in an element structure, development of a substance, and the like have been carried out in order to solve the problems. For example, a light-emitting element for which a compound that has a carbazole skeleton and an anthracene skeleton including a substituted or unsubstituted phenyl group and has an excellent carrier-transport property is used is disclosed (see Patent Document 1).